1. Field of the Invention
The present invention generally relates to a method for fabricating a zeolite film and, more particularly, to a method for fabricating an oriented zeolite film.
2. Description of the Related Art
A conventional method for protecting metal products against corrosion includes performing surface treatment on the metal products utilizing phosphates and chromates, prolonging service life of such metal products. However, RoHS (restriction of the use of certain hazardous substance in electrical and electronic equipments) has been enforced recently in many countries, restricting the use of certain chemicals, such as hexavalent chromium, lead and mercury, in electronic equipments and daily supplies. Accordingly, a new method for surface treatment of metal products, which covers metal products with zeolite film to slow down oxidation of the metal products, has been developed for years.
A conventional method for fabricating a zeolite film utilize wet hydrothermal method, which includes adding tetraethyl orthosilicate in aqueous solution of tetrapropylammonium hydroxide and stirring for 4 hours to obtain a precursor solution, pouring the precursor solution in a reaction chamber made of Teflon, immersing a metal substrate in the precursor solution, sealing the reaction chamber, and heating the reaction chamber to 180° C. to conduct a reaction to the metal substrate for at least 12 hours. As such, a conventional zeolite film is formed on the metal substrate.
Though the conventional zeolite film protects the metal substrate from environmental moisture and oxygen, slowing down the oxidation reaction of the metal substrate; however, since zeolite crystal is randomly stacked during the procedure of such conventional method, environmental moisture and oxygen are not completely blocked. In the case that excellent anti-corrosion ability is desired, the thickness of the zeolite film must be dramatically elevated correspondingly. That is, the conventional method cannot fabricate the zeolite film with a small thickness while having sufficient anti-corrosion ability. Moreover, a large amount of the precursor solution is required in the conventional method, such that the metal substrate can be immersed therein for uniformly conducting the reaction on all surfaces of the metal substrate. However, the basic precursor solution may cause corrosion of the metal substrate during the reaction, weakening the mechanical strength of the metal substrate. Besides, the precursor solution still contains the raw materials after the reaction, such as orthosilicate and tetrapropylammonium hydroxide, and becomes waste due to the difficulty of separation of these raw materials. The waste is accumulated imperceptibly during the fabrication procedure of the conventional zeolite film; therefore, the conventional method is on the other side against environmental protection.
In light of the above, it is needed to provide a method for fabricating a zeolite film which overcomes the above problems of the conventional method.